SD memory cards work by recording data onto a solid-state chip inside the card using flash memory. The flash memory records information when electrical charges change in its circuits. A similar process erases portions of the memory for rewriting.
SD is an abbreviation for "secure digital." The data on an SD card is stored in a digital format. The solid-state chip inside the card's plastic cover contains many tiny electrical circuits. When the card is not in use, the circuits retain their charges without any additional power. When a card is placed in an activated device, such as a camera or a cellphone, a small electrical current from the device moves electrons in the flash memory chip. The digital patterns stored on the chip correlate to the data stored there. Data is erased when a slightly higher voltage is applied to the circuit. This allows for rewriting. SD cards write and erase memory in blocks or sections. This makes them faster than some other varieties of data storage.
SD cards meet legal requirements for storing content with copyright protection. Copyright protected works, such as songs and books, are written with a media identifier code. That code is placed on a protected portion of the solid-state memory. The copyright protected work cannot be copied without access to that media identifier code. This keeps data from being copied multiple times and widely circulated without permission.